However, it appears that styles of elements I import and use from Polymer take precedent. So for example I may

create style in my mystyles.css

.my-background {
background: #4fc3f7;
}

and then apply it

paper-fab class="my-background"..>...

But the background of paper-fab is unaffected, being override by the style of paper-fab.

Apologies, as various articles do go along way to explaining the use of styles in Polymer. But none are explicit and simple enough to say "if you used to import styles in the past like this..... then now do it like so..."